α-Amino acids are the basic structural units of proteins and present in the chemical structures of many biologically important compounds. The alpha carbon of α-amino acids, when bonded to a non-hydrogen side chain, is a chiral center. Such amino acids, e.g., alanine, can be one of two stereoisomers, designated L- and D-. An amino acid's stereochemistry can influence a compound's biological properties, including, for example, maytansinoid's properties. Maytansinoids are cytotoxic compounds structurally related to the natural product maytansine. Maytansinoids include C-3 esters of maytansinol, such as C-3 amino acid esters of maytansinol and derivatives of the same. It has been reported that certain C-3 N-methyl-L-alanine esters of maytansinol are more cytotoxic than those of the corresponding D-form. Current methods of synthesizing stereomerically pure C-3 amino acids esters of maytansinol require multiple steps, involve low-yielding reactions, require hard-to-access reagents, and/or require purification steps to remove undesired stereoisomers. Thus, there is need for synthetic methods that efficiently install amino acids, e.g., to provide esters such as C-3 esters of maytansinol, with high stereomeric purity.